Treatment of spodumene



United States Patent 3,394,988 TREATMENT OF SPODUMENE John H. Fishwiek,West Chester, Pa., assignor to Foote Mineral Company, Exton, Pa., acorporation of Pennsylvania N0 Drawing. Continuation-in-part ofapplication Ser. No. 516,727, Dec. 27, 1965. This application Oct. 31,1967, Ser. No. 679,503

14 Claims. (Cl. 23-110) ABSTRACT OF THE DISCLOSURE fl-Spodumene whichhas been converted from oL- to ,8- form at a temperature of from about1850 F. to about 2100 F. is contacted with chlorine gas or hydrogenchloride at a temperature of at least 1750 F. to about 2100 F. until atleast a major portion of the lattice-bound iron therein is removed.

This application is a continuation-in-part of application Ser. No.516,727, filed Dec. 27, 1965.

The present invention relates to the treatment of spodumene; and, moreparticularly, the present invention relates to a process for removinglattice-bound iron from spodumene.

Spodumene is a naturally-occurring lithium aluminosilicate mineralwidely used as a source of lithia in ceramics. This material normallycontains a small amount of iron, and, as the result of crushing,flotation, magnetic separation and screening operations, the spodumeneavailable commercially may have iron contents ranging from about 0.6% toabout 2.5% (as Fe O Although reported as Fe O a portion of this ironcontamination may be free iron introduced from grinding operations.However, a substantial portion of the iron contamination is present insolid solution in the spodumene lattice, possibly taking the place of analuminum atom in the crystal structure.

Iron oxide is a particularly undesirable contaminant in glasses and inproducts made from glass (glass-ceramics). Even relatively small amountsof iron are often sufficient to impart an objectionable color to glassproducts or to products manufactured by way of the glassy state. As aresult, wide utilization of spodumene as a source of lithia by the glassindustry has not been realized.

To provide a spodumene material acceptable to the glass industry, theiron content would have to be substantially reduced. A reduction in ironfrom about 0.6% Fe O or above to about 0.1% Fe 0 or below would beconsidered very good and should lead to a product acceptable to theglass industry as far as iron contamination is concerned. Such a productwould have a Li O/Fe O weight ratio of about 70- or higher.

However, the removal of substantial iron from spodumene withoutdestroying the spodumenes structure or without removing lithia haspresented difiieulties. The difficulties are believed to be due to thefact that the iron is combined in the spodumene lattice as stated above.Thus, hot acids under pressure are not effective in removing ironcontamination without extracting lithia values at the same time, andmagnetic separation, either wet or dry, has not proved eflective inremoving the lattice-bound iron. One improved approach involves heatingthe spodumene in a reducing, hydrogen-containing atmosphere until atleast a major portion of the lattice-bound iron therein has beenconverted to elemental iron. The treated spodumene then is furthertreated as by acid leaching, to remove the reduced iron.

It has long been known that elemental iron will react with chlorine orhydrogen chloride to form a volatile iron chloride. Thus, the relativelyfree iron associated with sand and clay, for example, can be so reactedwith chlorine of hydrogen chloride (US. Patents Nos. 1,824,807 and2,182,384, British Patent No. 834,383 and German Patent No. 586,588).

It is the principal object of the present invention to provide asingle-step process for removing lattice-bound iron from spodumene.

It is another object of the present invention to provide a novel processfor reducing substantially the iron content of spodumene.

It is a further object of the present invention to provide a novelprocess for reducing substantially the iron content of spodumenewithout, at the same time, reducing significantly the lithia contentthereof.

Other objects will become apparent from a consideration of the followingspecification and claims.

The present process comprises heating oc-SPOdUIHCIle at a temperaturefrom about 1850 to about 2100 F. to convert it to fi-spodumene andcontacting the fi-spodumene with at least one chlorinous gas selectedfrom the group consisting of chlorine and hydrogen chloride at atemperature of from at least about 1750 to about 2100 F. until at leastthe major portion of the lattice-bound iron is removed.

The present process is a simple yet highly effective way to removelattice-bound iron contamination from spodumene. This iron may beremoved from the spodumene without significantly removing lithia values,and the process does not otherwise deleteriously affect the spodumene.Of importance is the fact that the present process may involve but asingle steptreatment with chlorine or hydrogen chl0rideand does notrequire a preliminary reduction treatment with hydrogen. This issurprising, in view of the prior art and the past difficulties inremoving lattice-bound iron from spodumene. As a result of the presentprocess, the iron content of commercial spodumene has been reduced to aslow as about 0.04%. As will appear hereinafter, the extent of ironremoval achieved in any particular case may depend upon various factors,such as temperature and time of treatment and extent of supplementalmagnetic separation of free magnetic iron compounds. However, suchfactors can be controlled as necessitated by the degree of reduction iniron contamination desired. As stated previously reduction of ironcontamination to below about 0.1% Fe O is the preferred goal, at leastto provide a product acceptable to the glassmaking industry. Otherapplications may not require such a high degree of iron removal so thatthe present invention may find use in applications where it is desiredto re duce the iron content to, say, about 0.3%.

Spodumene, which in its natural state is in the socalled alpha form,upon concentration by flotation contains in the neighborhood of 6.2% H 0and 2.5 Fe O This can be further refined by passing a slurry thereofthrough a permanent magnet which removes metallic iron and the morestrongly magnetic free iron compounds, lowering the Fe O content to theneighborhood of 1.5%, and, coincidentally, raising the Li O contentslightly, say to the neighborhood of 6.4%. This spodumene will bereferred to hereinafter as 1.5% Fe O grade spodumene. Roughly two-thirdsof the iron in this grade of spodumene is in the form of freeiron-containing compounds or minerals (e.g. amphiboles, triphyllite andchlorite) which are somewhat magnetic and can be removed physically asby high intensity magnetic separation followed by screen removal ofiron-rich fines. The resulting spodumene, referred to hereinafter asceramic grade spodumene, has a Fe O content in the neighborhood of 0.5-0.6%. Most of this iron, as distinguished from the free forms physicallyseparable from the spodumene as discussed above, is a chemical part ofthe spodumene itself.

It is unreduced, cationic iron, being in a positive valence state, atleast +2 and most likely +3. It is, as stated, in solid solution in thespodumene lattice, possibly taking the place of an aluminum atom in thealumino silicate crystal structure. It is this iron contamination thathas presented the greatest difficulties, and it is to the removal of atleast the major portion of this iron that the present invention isdirected. It has been found that, in fi-spodumene which has beenconverted from ato it-form at a temperature of from about 1850 to about2100 F., chlorine and hydrogen chloride will act directly on thislattice-bound iron, under certain temperature conditions, converting itto volatile iron chloride which. passes out of the spodumene and intothe gas atmosphere.

The spodumene should be finely-divided. Generally, it will be fineenough such that at least 90% thereof passes through a 4 mesh screen(US. Standard Series), preferably a 20 mesh screen.

In accordance with the present invention, a -spodumene which has beenconverted from ato ,B-form at a temperature from about 1850 to about2100 F., is contacted with chlorine and/ or hydrogen chloride at atemperature of at least about 1750 F. and up to about 2100 F. Apreferred temperature range for treatment with the chlorine or hydrogen.chloride is from about 1850 to about 2000 F. At these temperatures,appreciable sintering of the spodumene grains does not take place.Temperatures down to about 1750 F. are suitable when the statedpreconverted fl-spodumene is the starting material. When tZ-SPOdUITlCIlGis the starting material, the temperature should be at least about 1850F., as stated, and preferably from about 1850 to about 2000 F. to insureproper conversion thereof to B-form in the presence of the treating gas.It will be seen from the foregoing that conversion of the spodumene fromato ,B-form may take place prior to or during treatment with thechlorine and/ or hydrogen chloride.

The time at which the sopdumene is maintained in contact with thetreating gas at a temperature within these ranges does not appear to becritical and may well be determined by the nature of the equipment used.For example, in counter-current gas-solids contacting apparatus, theactual contact time may be a matter of seconds; in rotary kilns, it maybe somewhat longer, and in batch, fixed bed operations, it may be evenlonger, as up to about an hour. In any event, substantially eachindividual spodumene particle will be contacted by the chlorine orhydrogen chloride. The time required in any particular case can bereadily determined by analyzing samples from time to time.

Contact of the stated B-spodumene with the chlorine or hydrogen chloridecauses conversion of lattice-bound iron to volatile iron chloride. Inaccordance with the present invention, the time-temperature conditionsare generally selected to convert at least the major portion of thelattice-bound iron to iron chloride. The iron chloride, being volatileunder the temperature conditions employed, passes Off into the treatingatmosphere which eventually becomes separated from the treatedspodumene. The iron chloride may itself be separated from the atmosphereby selective condensations.

With respect to the chlorine and hydrogen chloride employed, this may beessentially the pure gas itself, that is, the treating atmosphere may besubstantially 100% chlorine, 100% hydrogen chloride or composed entirelyof a mixture of both. However, chlorine or hydrogen chloride need notdisplace all the air in the treating zone, and atmospheres much lessconcentrated in such gas may be used. Concentrations of chlorine andhydrogen chloride in air or other gas, like flue gas, down to about 5%,by volume, are possible depending upon the degree of reduction of ironcontent desired. Air containing from about to about chlorine, by volume,is the preferred chlorine-containing atmosphere. It will be noted thatthis treating atmosphere is actually oxidizing in the chemical sense sothat no reduction of the iron can take place during treatment.

Reference has been made above to the magnetic separation of free ironand free magnetic iron compounds or minerals from spodumene. While it isnot necessary that any of this magnetic material be removedmagnetically, advantageously at least the more highly magnetic materialis removed, as by wet separation using a premanent magnet, beforetreatment according to the present invention so that the startingmaterial has an iron content no greater than about 1.5% -(as F6203)-Preferably, even the less magnetic free iron compounds or minerals arealso removed by wet or dry high-intensity, induced roll magneticseparation. Surprisingly, this high intensity magnetic separation iseffective after treatment with chlorine or hydrogen chloride, althoughits greatest effect is prior to such treatment. In this latter case, theiron content of the spodumene starting material will be reduced to theneighborhood of 05-09% (as Fe og). depending upon the number of passesthrough magnetic separation, and the starting material is comparable toceramic grade spodumene.

The invention will be more fully understood from the following exampleswhich are given. for the purpose of illustration and are not intended tolimit the scope of the invention in any Way.

Examples 1-23 illustrate the use of chlorine gas.

Example 1 Ceramic grade tit-spodumene, 25 grams (about through 200 mesh)is placed in a refractory fire clay combustion boat and placed inside afused silica tube in an electrically heated furnace. The tube and itscontents are heated to 1900 F. After a brief nitrogen purge, chlorinegas is admitted to the tube and flowed through the tube for one-halfhour. The chlorine is then turned off, and the tube purged again withnitrogen. The original untreated spodumene has 7.04% Li O and 0.63% Fe O(Li O/Fe O ratio of 11.2); the final treated spodumene has 6.51% Li Oand 0.06% Fe O (Li O/Fe O ratio of 108.5). About 90-95% of thetat-spodumene is converted to fi-spodumene during the treatment.

Example 2 The procedure of Example 1 is followed except that theCL-SPOdUITlGHB has a particle size through 40 mesh, contains 6.73% Li Oand 0.71% re o (Li O/Fe O ratio of 9.5), and the temperature of chlorinetreatment is 1950 F. The product contains 6.49% U 0 and 0.07% R2 0 (LiO/Fe O ratio of 92.7). Over of the a-spodu mene is converted to betaform.

Example 3 The procedure of Example 1 is followed except that thespodumene is ceramic grade tit-spodumene obtained by pre-calcining thetat-spodumene of Example 1 in air at 2075 F., and the temperature ofchlorine treatment is 1950 F. The product contains 6.78% U 0 and 0.07%F203 (Li20/Fe203 ratio Of Example 4 The procedure of Example 3 isfollowed except that the temperature of chlorine treatment is 1750 F.The product contains 7.00 U 0 and 0.19% Fe O (Li O/Fe O ratio of 36.8).

Example 5 The procedure of Example 2 is followed except that thespodumene is ceramic grade fi-spodumene obtained by pre-calcining thetat-spodumene of Example 2 in air at 2075 F., and the temperature ofchlorine treatment is 2000 F. The product contains 6.33% M 0 and 0.04%Fe O (Li O/Fe O ratio of 158.3).

Example 6 The procedure of Example 5 is followed except that thetemperature of chlorine treatment is 1750 F. The product contains 6.63%Li O and 0.16% Fe O (Li O/Fe O ratio of 41.4).

Example 7 The procedure of Example 1 is followed except that thespodumene is 1.5% Fe O grade tat-spodumene (21.8%+80 mesh, 29.5%80+140mesh,

36.3% 140'+325 mesh 12.4%-325 mesh) containing 6.42% Li O and 1.61% Fe O(Li O/Fe o ratio of 3.99), and the temperature of chlorine treatment is2000 F. The product contains 5.56% Li O and 0.13% Fe O (Li O/Fe O ratioof 42.8). Essentially all of the tat-spodumene is converted to betaform.

Example 8 The procedure of Example 7 is followed except that thea-spodumene is preliminarily milled to where 65% passes a 325 meshscreen. The product contains 5.49% U and 0.09% Fe O (Li O/Fe O ratio of61).

Example 9 In this example is used 1.5% Fe O grade a-spodumene (6.43% U 0and 1.54% Fe O having the particle size distribution: 18.1%+80 mesh,33.8%-80+140 mesh, 19.8%-140+200 mesh, 17.8%200+325 mesh and 10.5% -325mesh. Seventy-five grams, held in an alumina :boat, are placed in afused silica tube (72" x 3") held in an electrically heated furnace. Thetube and its contents are heated to 1950 F. Chlorine gas is then passedinto and through the tube displacing the air, and the passage ofchlorine through the tube is continued for 30 minutes at the rate of1.36 ftfi/hr. The treated spodumene contains 6.05% Li O and 0.35% Fe OAfter being subjected to slight vibration to separate black specks offree iron compounds or minerals from the spodumene particles, thematerial is subjected to dry high intensity, induced roll magneticseparation (two passes) resulting in a nonmagnetic fraction (amountingto 87.13% of the starting material) containing 6.18% U 0 and 0.10% E2 0Example 10 In this example, the spodumene as used in Example 9 issubjected to dry, high intensity, induced roll magnetic separation (onepass) and a sample is treated with chlorine under the same conditions asin Example 9. This product contains 6.43% Li O and 0.12% Fe O Theremainder of the material from which the sample is taken is subjected toanother pass of high intensity magnetic separation to provide a materialcontaining 6.83% Li O and 0.57% Fe O This material is then subjected tochlorination under the same conditions as in Example 9 to provide aproduct containing 6.47% Li O and 0.06% F203.

Examples 11-17 Spodumene as used in Example 9 is subjected to highintensity magnetic separation (two passes) to provide a materialcontaining 6.73% U 0 and 0.64% Fe O Samples of this material are thentreated with chlorine as in Example 9 but for different times and atdifferent temperatures as set forth in the following Table I along withthe U 0 and Fe O contents of the treated products.

TABLE I Example Temp. F.) Time (min) Li20 F0203 (percent) (percent) 6Examples 18-21 In these examples, the tat-spodumene of Example 2 iscalcined in air to fi-spodumene at 2075 F. Twenty-five gram lots of thismaterial are treated'at 1950 F., with various mixtures of chlorine andair for various periods of time as set forth in the following Table IIalong with the Li O and Fe 0 contents of the treated products:

TABLE 11 Example Chlorine Air Time L120 F6203 (percent) (percent) (111'(percent) (percent) The following examples illustrate the use ofhydrogen chloride.

Examples 22-33 Ceramic grade a-spodumene (20 x 140 mesh) is calcined for/2 hour at various temperatures set forth in the following Table III asthe Cale. Temp. Samples of the resulting B-spodumene, 4 grams each, arechanged to an alumina combustion boat which is placed inside a fusedsilica tube in an electrically heated furnace. Hydrogen chloride is thenpassed through the tube at a flow rate of 1.36 ft. /hr. for /2 hour atvarious temperatures set forth in the following Table III as Treat.Temp. The original untreated spodumene has 6.91% U 0 and 0.55% Fe O (LiO/Fe O ratio of 12.4); and the final treated spodumene has values as setforth in Table III.

TABLE III Ex- Cale. Treat. L FezO; LizO/ ample Temp. F.) Temp. F.)(percent) (percent) F620 Examples 34-3 8 Samples of tar-spodumene asused in Examples 22-23, but which has not been converted tofi-spodumene, are treated with hydrogen chloride as in Examples 22-23 atvarious temperatures with the results set forth in the following TableIV.

TABLE IV Example Treat. Temp. L120 F9203 Liz0/Fe2O F.) (percent)(percent) The product of Example 34 is only about 10% converted to 5form; that of Example 35 is about 85-90% converted, and those ofExamples 36-38 are essentially completely converted.

Examples 39-41 Alpha-spodumene as used in Examples 22-28 is calcined at1900 F. for V2 hour converting 85-90% thereof to ,8 form. Samples of thecalcined material are then treated with mixtures of hydrogen chlorideand carbon dioxide, as set forth in the following Table V, at

7 2000 F. for /2 hour and at a total flow rate of 5 ft. hr. The resultsare as follows:

TABLE V Example H01 CO2 L120 FczOa LizO/ (percent) (percent) (percent)(percent) FezOa Modification is possible in the selection of operatingtechniques and conditions without departing from the scope of theinvention.

Examples 42-54 Samples of ceramic grade spodumene (6.90% Li O; 0.55% FeO previously calcined at 1900" F. for 1 hour, are subjected to variousgases and gas mixtures at 1900 F. in a 1' LD. mullite tube in a closedsystem. The gas flow is 1.5 ft. hr. The values of the treated spodumeneThe gas mixtures were selected as being typical mixtures obtained onburning a hydrocarbon or carbon (e.g. coke) in the presence of chlorineand various proportions of oxygen.

What is claimed is:

1. The process for removing latticebound iron from spodumene whichcomprises heating a-spodumene at a temperature from about 1850 to about2100 F. to convert it to fi-spodumene and contacting the fl-spodumenewith at least one chlorinous gas selected from the group consisting ofchlorine and hydrogen chloride at a temperature of from at least about1750 to about 2100 F. until at least the major portion of thelattice-bound iron is removed.

2. The process of claim 1 wherein the fl-spodumene is contacted withsaid gas until the lattice-bound iron content is reduced to below about0.3% (as Fe O 3. The process of claim 2 wherein the S-spodumene iscontacted with said gas until the lattice-bound iron content is reducedto no more than about 0.1% (as Fe O 4. The process for removinglattice-bound iron from spodumene which comprises heating OL-SPOdUmBHCat a temperature from about 1850 F. to about 2100 F. to convert it tofl-spodumene and contacting the p-spodurncne with chlorine gas at atemperature of from at least about 1750 to about 2100 F. until at leastthe major portion of the lattice-bound iron is removed.

5. The process of claim 4 wherein the fi-spodumene is contacted with thechlorine until the lattice-bound iron content is reduced to below about0.3% (as Fe o 6. The process of claim 5 wherein the fl-spodurnene iscontacted with the chlorine until the lattice-bound iron content isreduced to no more than about 0.1% (as F6203).

7. The process of claim 4 wherein said spodumene contains free magneticiron compounds and wherein at least a substantial portion of these isremoved magnetically prior to contact with said chlorine.

8. The process of claim 4 wherein said fi-spodumene, following saidcontact with chlorine and removal of lattice-bound iron, contains freemagnetic iron compounds and wherein at least a substantial portion ofthese is removed magnetically.

9. The process of claim 4 wherein said fl-spodumene is contacted withsaid chlorine gas at a temperature of from about 1850 to about 2000 F.

10. The process of claim 1 wherein said gas is hydrogen chloride.

11. The process of claim 2 wherein said gas is hydrogen chloride.

12. The process of claim 3 wherein said gas is hydrogen chloride.

13. The process of claim 10 wherein said spodumene contains freemagnetic iron compounds and wherein at least a substantial portion ofthese is removed magnetically prior to contact with said hydrogenchloride.

14. The process of claim 10 wherein said ,B-spodumene, following saidcontact with hydrogen chloride and removal of lattice-bound iron,contains free magnetic iron compounds and wherein at least a substantialportion of these is removed magnetically.

References Cited.

UNITED STATES PATENTS 1,824,807 9/1931 English 23-110 X 2,182,38412/1939 McGregor 23182 X FOREIGN PATENTS 834,383 5/1960 Great Britain.

OSCAR R. VERTIZ, Primary Examiner.

A. GRIEF, Assistant Examiner.

